McQuay IM 777-4
25
Service and Maintenance
MVP Variable Speed Sheaves
Mounting
1
Verify both driving and driven sheaves are in alignment
and the shafts are parallel. The centerline of the driving
sheave must be in line with the centerline of the driven
sheave. See
Figure 37, page 26
.
2
Verify that all setscrews are torqued to the values shown
in
Figure 17, page 25
before starting drive. Check
setscrew torque and belt tension after 24 hours of
service.
Adjusting
1
Adjust motor base forward to release belt tension.
Remove the belts for easier adjustment.
2
Loosen, but do not remove both of the locking setscrews
A
in the outer locking ring by using a hex key or torque
wrench with a hex bit.
3
Adjust sheave to desired pitch diameter by turning the
outer locking ring. Use a spanner wrench or drift inserted
into the three holes that are located 120° apart on the
ring.
4
Any pitch diameter can be obtained within the sheave
range. One complete turn of the outer locking ring
changes the pitch diameter 0.233".
5
Do not open sheaves more than the following:
a
Do not open
B
sheaves more than 4 3/4 turns for the
A
belts or 6 turns for the
B
belts.
b
Do not open
C
sheaves more than 9 1/2 turns.
c
Do not open
5V
sheaves more than 6 turns.
d
Do not open
8V
sheaves more than 8 turns.
6
Tighten BOTH locking screws
A
in the outer locking
ring before operating the drive. Use a torque wrench and
tighten to the value shown in
Table 17
.
7
Replace belts and adjust the motor base to tension the
belts properly. See
Fan Drive Belt‚ page 26
.
8
Do not loosen any screws other than the two locking
screws
A
in the outer locking ring when adjusting the
sheave pitch. Do not operate the drive until the locking
screws have been set to the torque specifications.
Table 17: Screw Torque Values
Nominal screw size
(dia–-thds/in)
Socket head cap screws
Flat head socket
screws
Hollow head set screws only
Lengths equal or greater than dia.
For lengths (L)) less than dia.
Seating torque
Seating torque
Seating torque
Seating torque
Length (L)
Seating torque
(in–lbs)
(in–lbs)
(in–lbs)
(in–lbs)
(in–lbs)
(in–lbs)
(in–lbs)
1/4–20NC
150
12.5
100
87
7.3
3/16
50
5/16–11NC
305
25.4
200
165
13.8
1/4
90
3/8–16NC
545
45.4
350
290
24.2
1/4, 5/16
150, 250
1/2–13NC
1300
108.3
N/A
620
51.7
N/A
N/A
5/8–11NC
N/A
N/A
N/A
1225
102.1
N/A
N/A
